In devices which operate at elevated internal temperatures, for example, a solid oxide fuel cell (SOFC) or a hydrocarbon catalytic fuel reformer operating at, for example, 900° C., it can be important for monitoring and control purposes to determine continuously the internal temperature. In the prior art, thermocouple devices typically are used to measure such elevated temperatures. However, thermocouples are known to have low signal output and to be significantly non-linear in their response, requiring special conditioning of the signal for meaningful measurement. Further, the signal is vulnerable to electrical noise in practical applications. Also in the prior art, thermistors or resistance temperature devices (RTDs) are known to be operationally superior to thermocouples, but the problem with these devices is that they typically are limited to temperatures of less than about 300° C.
What is needed is an improved apparatus, having substantially linear response, and method for determining accurately any temperature within a range of temperatures, especially temperatures elevated beyond the range of measurement for thermistors and RTDs.
It is a principal object of the present invention to provide an improved method and apparatus for determining elevated temperatures.
It is a further object of the invention to provide such apparatus and method wherein such elevated temperature is characteristic of a region not readily accessible to prior art temperature measuring means.
It is a still further object of the invention to provide such apparatus and method which can reliably provide continuous determination of the internal temperature of a fuel cell or hydrocarbon reformer.